About Frilled Sharks
Frilled sharks, (Chlamydoselachus anguineus), are an uncommon primitive shark species typically found near the sea floor in waters over outer continental and island (insular) shelves and upper slopes, usually at depths between 120 and 1,280 m but up to 1,570 m and occasionally even at the surface.
The frilled shark is a strange, prehistoric-looking shark that lives in the open ocean and spends much of its time in deep, dark waters far below the sea surface. Its long, cylindrical body reaches lengths of nearly 7 feet (2 m), and its fins are placed far back on the body. The frilled shark gets its name from the frilly appearance of its gill slits.
Frilled sharks are active predators and may lunge at potential prey, swallowing it whole, even if it is quite large. Their normal swimming style, however, is distinctly eel-like, as they swim in a serpentine fashion. The preferred prey of the frilled shark is squid, and they have several rows of long teeth, each with three long points, that are perfect for snagging the soft bodies of this prey. Though they specialize on squids, frilled sharks are known to eat a variety of fishes and also other sharks.
Frilled sharks are only very rarely encountered in the wild, so little is known about their ecology. The limited information that scientists do have is based on dissection of individuals captured in deep-sea net fisheries and observation of the occasional live individual in captivity. Frilled sharks reproduce via internal fertilization and give live birth. However, they do not connect to their young through a placenta, like in most mammals. Instead, embryos live off of energy obtained from yolk sacs, and only after the juveniles are able to survive on their own does the mother give birth to her young.
Little is known about the population trends of frilled sharks, but they are rarely encountered by humans and are likely naturally rare. In some places they are accidentally caught as by catch in fisheries targeting other species, and in these cases, they may be kept and used as food. No fisheries specifically target frilled sharks. Experts as a result of their natural rarity and occasional capture in some fisheries consider the frilled shark to be near threatened with extinction.
The frilled shark was first scientifically recognized by German ichthyologist Ludwig doderlein, who visited Japan between 1879 and 1881 and brought two specimens to Vienna. However, his manuscript describing the species was lost, so the first description of the frilled shark was authored by American zoologist Samuel Garman, working from a 1.5-metre (4 ft 11 in)-long female caught from Sagami Bay in Japan. His account, “An Extraordinary Shark”, was published in an 1884 volume of Proceedings of the Essex Institute.
At depths between 160 to 660 feet (50 to 200 meters) in Sugar Bay, Japan, Frilled Sharks eat mostly squids. A recent study revealed that they eat not only weak-swimming deep-sea squids but also some surprisingly fast and powerful mesopelagic varieties. Although the study found that cephalopods compose about 61 percent of Frilled Shark diet, it also showed that a further 11 percent is composed of various teleost fishes. While the squids could be identified, often to species, based on their chitinous beaks, teleost prey was in a state of digestion too advanced to allow identification to species or even family. There is also a report of a 5.3-foot (1.6-meter) Frilled Shark from coastal waters off Choshi, Japan, that had in its stomach a 21-ounce (590-gram) Japanese Catshark (Apristuris japonicus). Thus, Frilled Sharks capture prey near the bottom as well as far above it.
One aspect of Frilled Shark biology that recently became a little less mysterious is reproduction. A study of 264 Frilled Sharks from Saruga Bay, Japan, found that here this species breeds year-round, producing an average litter of 6 pups, each about 22 inches (55 centimeters) long. It is hardly surprising that Frilled Shark litters are typically rather small, given this species slender build. In fact, the female Frilled Shark has a trunk proportionately longer than that of the male, presumably to make room for developing young in a remarkably attenuate body. But what is downright astonishing is the duration of the gestation period, estimated to be as much as 42 months (3.5 years). If this is correct, the gestation period of the Frilled Shark is nearly twice as long as that of an African Elephant (22 months) and by far the longest of any vertebrate animal.